The invention relates to antenna configurations and more particularly to antennas for operating in the ultrahigh and above frequency bands, covering an octave or more in bandwidth and having substantially omnidirectional radiation/reception characteristics.
There are applications for transmitting and/or receiving antennas that are highly efficient, capable of operating over a bandwidth of an octave or more, and are omnidirectional, that is, have substantially uniform transmission and reception characteristics in three dimensional space, as compared to the more usual antenna design which seeks high gain in a particular direction or directions. For example, these properties are desirable in certain types of antennas carried by aircraft for communication and surveilance. The substantially omnidirectional characteristics of the antenna allow reception and transmission at uniform signal levels in nearly all directions in the three-dimensional airspace surrounding the center of the aircraft antenna. The broadband feature permits the antenna to operate effectively over a wide spectrum of frequencies without the limitations that accompany tuned, narrow band antennas and antennas of only moderate bandwidth, i.e., substantially less than an octave.
Thus, one purpose of the invention is to provide an aircraft-carried antenna having the omnidirectional and wideband properties. Furthermore, it is desirable to have an antenna configuration that is easily deployed from the aircraft body, such as by means of a trailing wire passed through an opening in the body and towed by the aircraft. The antenna structure, when connected to such a trailing wire, should have a geometry that creates minimal aerodynamic drag and has stable flight characteristics.
Although numerous antenna designs exist for a wide variety of applications including, in some cases, antennas that exhibit certain, but not all of the features noted above, none have been found completely suited to the above requirements. A common shortcoming of existing antenna structures is their narrow band properties, in which the antenna has been carefully constructed to operate over a selected, relatively narrow bandwidth or, in other words, a tuned antenna. Also, most available antennas are designed with a moderate to high gain to focus the transmission and reception of the antenna in a particular direction or directions, whereas in the present application a wholly nondirectional (or omnidirectional) characteristic is desired. Still another disadvantage of existing antenna designs that might otherwise satisfy at least some of the above-noted requirements, is the manufacturing cost of such special-purpose antenna configurations. The more exotic the antenna geometry becomes, the greater the cost of manufacture. Also, the antenna design may attain some of the features desired, but prove very inefficient and/or cumbersome and, hence, impractical.